1. Field of the Invention
The present invention relates to the field of lightweight, pocket-sized or portable scales and improvements thereto.
2. Description of Related Art
Portable balance beam scales with integrated carrying cases are well known in the art. A typical scale includes a fulcrum projecting from a base, which may double as the bottom half of the carrying case, as disclosed, for example, by U.S. Pat. No. 4,744,428 to KNOTTER et al. and U.S. Pat. No. 3,968,849 to DALE et al. The typical scale also includes a balance beam positioned across the fulcrum, with a load pan on one end and a graduated scale on the other end. The pan and the graduated scale are disposed on opposite sides of the fulcrum, so that a slidable weight (or weights) can be moved along the balance beam in order to balance the load in the pan. When the load pan and the slidable weight are in equilibrium (i.e., the balance beam is balanced in a horizontal position), the weight of the load in the load pan is equal to the number (or numbers) on the graduated scale next to which the slidable weights are positioned.
The prior art also includes a type of scale that incorporates a balance beam with a load pan on one side of a fulcrum and a weight pan on the other side of the fulcrum, as disclosed, for example, by U.S. Pat. No. 4,050,531 to ASHBROOK. In a portable scale having this design, a load to be weighed is placed in the load pan and balancing weights of known mass are placed in the weight pan, until the pans are in equilibrium (i.e., the beam is horizontally balanced) across the fulcrum. The weight of the load is then determined to be equal to the sum of the balancing weights.
To be effective, a portable sliding weight scale must be balanced whenever the sliding weight is set in the zero position. Achieving an appropriate balance is problematic for a portable scale because the load pan must be as lightweight as possible to keep the overall weight of the scale at a minimum. Therefore, a measuring weight positioned on the balance beam opposite the load pan must be light weight as well, or the scale will not be in equilibrium when the load pan is empty and the measuring weight is in the zero position. However, the measuring weight must be heavy enough to accurately weigh loads up to several grams or ounces in order to have practical use.
One attempt to address the zero position balancing problem in the prior art was to place the bulk of the measuring weight in a vertical plane of the fulcrum whenever the measuring weight is in a zero position, as in U.S. Pat. No. 4,744,428 to KNOTTER et al. The positioning prevents the measuring weight from factoring into the balancing of the empty load pan. However, to position the measuring weight in the scale""s fulcrum requires a convoluted design of the measuring weight housing because, while the bulk of the weight is positioned in a plane of the fulcrum, an indicator of the weight must be adjacent to the zero position on the sliding scale. The additional material and the unorthodox design for the measuring weight housing increase manufacturing costs.
Digital scales are also known in the prior art. Digital scales have many features, including an easy to read and precise display of the article weight. One such digital scale is disclosed, for example, by U.S. Pat. No. 3,698,493 to YAMANAKA et al. The YAMANAKA et al. scale includes a cradle for supporting the article to be weighed, a system of links, a spring having a spring force that balances the weight of the article, a code plate disc and a photoelectric element for reading the change in the link system caused by the weight of the article. The device includes a code generator for processing the output of the photoelectric element, and a digital indicator for displaying the weight in digital form.
Another digital scale is disclosed, for example, by U.S. Pat. No. 4,858,709 to STAHL. The STAHL device includes a weighing cell, an analog/digital converter for converting the signal of the weighing cell, and a microprocessor for receiving a signal from the analog/digital converter, and calculating and displaying the weight of the article.
Another digital scale is disclosed, for example, by U.S. Pat. No. 4,494,620 to KNOTHE et al. The KNOTHE et al. device incudes a load pan for receiving the article to be weighed, a liquid filled container having a gas bubble, a photosensitive receiver for detecting the position of the gas bubble (which position is dependent on the weight of the article), a digitizer, and a microprocessor for converting the digitized value to a weight measurement.
A disadvantage of the prior art is the absence of portable digital balance beam scales. The prior art analog portable scales can be difficult to read, due to the small size of the device. However, a digital scale is easy to read, with a clear liquid crystal display.
Another disadvantage of the prior art is the lack of precision of a weight reading on an analog scale. In the analog scale, it is difficult to obtain a precise measurement of the weight of the load, due to the size of the graduations on the scale, and the pointer on the dynamic weight. However, in a digital scale, the liquid crystal display digital reading gives a precise weight value.
The present invention is directed to a portable digital readout scale, which addresses the problems existing in the prior art, discussed above.
An aspect of the present invention provides a portable scale including a fulcrum, a balance beam pivotally mounted on the fulcrum, the balance beam supporting a load pan on one end and including an elongated portion having a measurement strip thereon extending from a first end toward a second, opposite end of the elongated portion of the balance beam, wherein the fulcrum is positioned between the load pan and the first end of the elongated portion, and a dynamic weight movable along the balance beam from the first end to the second end of the elongated portion of the balance beam, the dynamic weight including a display unit on the elongated portion of the balance beam for detecting the location of the dynamic weight along the measurement strip, for electrically converting the location to a weight measurement, and for displaying the weight measurement.
According to a further aspect of the present invention, the portable scale may further include a thumb wheel mounted on the balance beam, a stop mounted on the second end of the elongated portion of the balance beam, an elongated spindle having two ends, one of the two ends of the spindle being mounted in the thumb wheel for turning therewith, and the other of the ends being mounted at the stop, and a nut mounted on the dynamic weight for engagement with the spindle, wherein the dynamic weight can be moved along the elongated portion of the balance beam by turning the thumb wheel and the spindle therewith, which in turn moves the nut and the dynamic weight along the balance beam. In the portable scale of the present invention, the nut may further include a half nut and the dynamic weight may further include a pivot having a pivot axis perpendicular to the axis of the elongated spindle such that the dynamic weight can be pivoted about the pivot axis to lift the half nut off the spindle, to make coarse weight adjustments. In the portable scale of the present invention, the dynamic weight may further include a pair of slider bases for engagement with the sides of the balance beam and a bracket for holding the nut, such that the pair of slider bases slides along the edges of the balance beam as the nut and the dynamic weight move along the balance beam.
According to a further aspect of the present invention, the dynamic weight is removable and replaceable, enabling variations in a measurement range of the portable scale.
According to a further aspect of the present invention, the dynamic weight may further include a push button for resetting the weight measurement to zero. The portable scale of the present invention may further include a dynamic weight having a push button for switching between different systems of measurement.
In a further aspect of the present invention, a portable scale is provided including a base, a pair of fulcrum posts projecting from the base, a balance beam pivotally supportable on the pair of fulcrum posts, the balance beam including a load pan support member on one end and an elongated portion having a measurement strip thereon extending from the first end toward a second, opposite end of the elongated portion, the pair of fulcrum posts positioned between the load pan support member and the first end of the elongated portion of the balance beam, a load pan pivotally supported by the load pan support member, a dynamic weight member movably mounted on the balance beam for movement along the elongated portion, the dynamic weight including a display unit on the elongated portion of the balance beam for detecting the location of the dynamic weight member along the measurement strip, for electrically converting the location to a weight measurement, and for displaying the weight measurement, and a stationary counter weight attached to the load pan support member, wherein the stationary counter weight balances against the dynamic weight member when the dynamic weight is located at a zero position of the measurement strip on the balance beam.
According to a further aspect of the present invention, the portable scale may further include a carrying case, the carrying case including a top portion and a bottom portion, the top portion being closable onto the bottom portion and wherein the bottom portion includes the base of the portable scale.
According to a further aspect of the present invention, the measurement strip may include a printed circuit board having a pattern thereon for indicating the location of the dynamic weight member along the balance beam.
According to a further aspect of the present invention, the measurement strip may include an inlayed strip of copper or glass and a pattern etched into the inlayed strip for indicating the location of the dynamic weight member along the balance beam.
According to a further aspect of the present invention, the portable scale may further include luminescent material. The portable scale of the present invention may further include plastic material having luminescent pigment therein. The portable scale of the present invention may further include plastic material having phosphorescent material therein. The portable scale of the present invention may further include material which glows under ultraviolet light.
According to a further aspect of the present invention, a portable scale and carrying case combination is provided including a portable scale, and a carrying case for holding the portable scale, wherein the carrying case includes luminescent material. The portable scale and carrying case combination may further include a carrying case including plastic material having luminescent pigment therein. The portable scale and carrying case combination may further include a carrying case including plastic material having phosphorescent material therein. The portable scale and carrying case combination may further include a carrying case including luminescent material which glows under ultraviolet light.
According to a further aspect of the present invention, the portable scale and carrying case combination includes components for weighing a load, wherein the components include luminescent material. The portable scale and carrying case combination of the present invention may further include plastic having luminescent pigment therein. The portable scale and carrying case of the present invention may further include plastic material having phosphorescent material therein. The portable scale and carrying case combination of the present invention may further include material which glows under ultraviolet light.